1. Field of the Invention
The invention relates to an X-ray examination/diagnostic apparatus including an X-ray source and an X-ray image detection device which are mutually displacable with respect to an object to be examined, and more particularly, to a method and apparatus for controlling such mutual movement to comprise a continuous sweep during an X-ray examination of e.g., the vascular system of a patient.
2. Description of the Prior Art
X-ray examination apparatus for vascular imaging are now widely used and well known in the literature e.g. from U.S. Pat. No. 4,204,225 entitled REAL TIME DIGITAL X-RAY SUBTRACTION IMAGING. In such a device for digital subtraction imaging, X-ray images of a portion of a patient are recorded both before a contrast medium is injected into the patient as well as after injection of the contrast medium into the patient. Both sets of images are stored and digitized and then processed so that the images without the contrast medium (referred to hereinafter as mask images) are subtracted from the contrast-filled images (referred to hereinafter as contrast images) with a result that the contrast-filled vascular system becomes highly visible upon display of the processed images. During examination of, for example, parts of the body of the patient which do not fit within a single image field of the X-ray image detection device, problems are encountered because the images must be acquired from a plurality of different locations along the length of the patient. Often difficulties are experienced with respect to actually acquiring images of the bolus of the contrast medium as it passes through the vascular system.
Known systems for use in such examinations include programmable stepping tables or gantrys which provide the required relative movement between the X-ray examination device and the patient in order that the bolus of the contrast medium can be followed and imaged as it moves through the vascular system. In such a system, the bolus of contrast medium can be introduced by a single injection and multiple X-ray images can be acquired both before and after the injection. For example, first a series of mask images can be taken across the entire part of the body to be examined, after which the contrast medium is administered and a series of contrast images are formed at preprogrammed stepped locations which correspond to the locations where the mask images were formed and hopefully, image the contrast medium as it progresses through the body. However, the acquired images occasionally miss imaging of the contrast bolus and the patient must be subjected to re-takes of the examination. This is undesirable because a re-take of the examination requires the patient to be subjected to an additional dose of contrast medium, and its attendant risks. One source of difficulty comes from the fact that the system operator may mis-judge the flow rate of the contrast medium in the patient and select an incorrect stepping program. Another source of difficultly is that when imaging the legs, e.g., one leg may have a faster flow rate than the other.
Although a leg-sized film can be used for performing this type of examination, the size of the film makes its handling inconvenient and the image quality is degraded as compared to digital image acquisition techniques, due to uneven X-ray exposure. Additionally, it is desirable to utilize digital subtraction angiography in order to limit the amount of X-ray exposure to the patient.
It is an object of the invention to enable either digital angiography or digital subtraction angiography examinations for larger parts of the body, wherein the longitudinal dimension of the object being imaged is larger than the optical input of the X-ray image detection device and where a mutual longitudinal displacement of the X-ray source and X-ray image detection device with respect to the object being imaged is controlled in a manner which ensures to a high degree that the propagation of the contrast medium bolus flowing through the object can be properly imaged.